Electric motors have applications where they are used in potentially hazardous environments. For instance, an electric motor may be used to drive mixers or pumps in environments where a risk of fire or explosion is normally present. Examples of such flammable environments can include pharmaceutical plants, such as where alcohol is used, chemical plants and food processing plants, such as grain plants. In such environments, pertinent standards and regulations can govern the types of electric motors than may be used. For example, Articles 500-504 of the NFPA 70 (National Electric Code) and Underwriter's Laboratories, Inc. Standard for Safety 674 set forth requirements for apparatus (which would include electric motors) to be used in “Hazardous Locations.” The standards and regulations can require that the electric motor be enclosed in a case that is capable of withstanding an internal explosion of a gas or vapor and of preventing the ignition of a gas or vapor surrounding the case, such as by sparks, flashes, or explosion of the gas or vapor within the case. An additional requirement may be that the electric motor will operate at an external temperature that a surrounding flammable atmosphere will not be ignited by the electric motor. Such electric motors may be called “explosion-proof” motors.
A typical electric motor for use in hazardous environments has a housing including a cylindrical casing and a pair of end caps. Disposed within the housing is a rotor attached to a shaft. A stator surrounds the rotor. Electrical current is provided to the rotor and the stator in a manner which causes the rotor, and hence the shaft, to rotate relative to the stator. The casing is held between the pair of end caps using external, longitudinally-extending bolts, each extending between aligned ears of the end caps. One end of the shaft extends through one of the end caps for attachment to operating equipment, such as a mixer or pump. An opposite end of the shaft extends through the other of the end caps and may have a fan attached thereto for purposes of providing circulation for cooling the motor. A fan shroud may be attached to the other of the end caps for covering the fan. A generally rectangular terminal box may be attached to the exterior of the casing.
Environments where it is desirable to use an explosion-proof motor may also be environments where it is desirable to use an electric motor than can be easily cleaned. However, typical electric motors for use in hazardous environments, such as those described above include complex exterior geometries that can render the motors difficult to clean. In some instances, the complex exterior geometries can result in hard-to-reach areas where bacteria can be difficult to remove, a particular disadvantage in applications in the food and pharmaceutical industries. Some of the complex geometries in typical explosion-proof motors include the external tie bolts, the ears associated with the external tie bolts and the shape of the terminal box.